A following ink-jet recording head has been put to practical use. Specifically, in the ink-jet recording head, a part of pressure generating chambers communicating with nozzle orifices for ejecting ink droplets is formed of a vibration plate, this vibration plate is deformed by piezoelectric elements, ink in the pressure generating chambers is pressurized and thus the ink droplets are ejected from the nozzle orifices. For example, as the ink-jet recording head described above, there is one in which a uniform piezoelectric material layer is formed over an entire surface of the vibration plate by use of a deposition technology, this piezoelectric material layer is cut into a shape corresponding to pressure generating chambers by use of a lithography method and piezoelectric elements are formed so as to be independent for each of the pressure generating chambers. There is a problem that such piezoelectric elements are prone to be damaged due to external environments such as moisture (humidity). For example, in a reservoir that is a common liquid chamber of the pressure generating chambers, ink containing moisture is filled. Thus, it is required to secure a certain distance between the reservoir and the piezoelectric elements.
Here, as a structure for preventing such damage to the piezoelectric elements, Japanese Patent Laid-Open No. 2000-296616, for example, discloses a structure in which a reservoir forming plate having a piezoelectric element holding portion is joined with a passage-forming substrate having pressure generating chambers formed therein, and piezoelectric elements are sealed in this piezoelectric element holding portion. Specifically, the structure includes: a passage-forming substrate in which a plurality of pressure generating chambers communicating with nozzle orifices are provided; piezoelectric elements which cause pressure changes in the respective pressure generating chambers; a reservoir forming plate in which a reservoir portion constituting at least a part of a reservoir, that is a common liquid chamber of the pressure generating chambers, is provided; and a nozzle plate which is joined with an opposite surface side of the passage-forming substrate and has nozzle orifices. In addition, in a region of the reservoir forming plate which faces the piezoelectric elements, a piezoelectric element holding portion is provided, which, in a state of securing a space without inhibiting movement of the piezoelectric elements, can seal the space. Note that, at one end of the respective pressure generating chambers in a longitudinal direction, ink supply paths for supplying ink in the reservoir to the respective pressure generating chambers are provided.
However, even in the above-described head structure in which the piezoelectric elements are formed in the piezoelectric element holding portion, the piezoelectric elements are likely to be damaged by moisture contained in the ink in the reservoir if the moisture permeates a junction portion between the passage-forming substrate and the reservoir forming plate and enters into the piezoelectric element holding portion. Therefore, in either case, it is required to secure a sufficient distance between the piezoelectric elements and the reservoir portion, more specifically, a sufficient length of a junction portion between the piezoelectric element holding portion and the reservoir. Meanwhile, in order to improve an ink supply property, it is required to shorten a length of the ink supply path. Thus if sufficiently securing the junction portion between the piezoelectric element holding portion and the reservoir is attempted, a space formed of only the passage-forming substrate is formed along an arrangement direction of the pressure generating chambers between the ink supply paths and the reservoir.
In the ink-jet recording head having the structure as described above, in: ejection of the ink, because of pressure changes caused in the pressure generating chambers, the ink in the pressure generating chambers flows out toward the reservoir through the ink supply paths simultaneously with the ink ejection. Thus, if there exists the space formed of only the passage-forming substrate between the respective ink supply paths and the reservoir, the ink flowing out toward the reservoir from the respective pressure generating chambers flows in both directions within the space, including the arrangement direction of the pressure generating chambers (a nozzle arrangement direction) and the longitudinal direction of the pressure generating chambers (a direction orthogonal to the nozzle arrangement direction). Thus, there is a problem that flows of the ink flowing out from adjacent pressure generating chambers interfere with each other to cause a so-called crosstalk and a stable ink ejecting property cannot be obtained.
Note that, if the junction portion between the piezoelectric element holding portion and the reservoir is shortened in accordance with the length of the ink supply path, a junction area between the passage-forming substrate and the reservoir forming plate is reduced. Thus, sufficient junction strength cannot be obtained. Moreover, if the ink supply path is formed to be relatively long in order to secure the junction portion between the piezoelectric element holding portion and the reservoir, a cross-section area of the ink supply path is substantially increased. Thus, there arises a problem that a damping property of meniscus is lowered and high-speed drive becomes impossible to perform.
Note that, needless to say, such problems as described above similarly exist not only in the ink-jet recording head for ejecting ink but also in another liquid jet head for ejecting a liquid other than ink.